A typical phantom (or inline) power communications system includes power-sourcing communications equipment and a set of remotely-powered network devices that connect to the power-sourcing communications equipment though a set of network cables. The power-sourcing communications equipment includes a power supply and transmit/receive circuitry. During operation, the power supply provides power to the remotely-powered network devices through the network cables, and the transmit/receive circuitry concurrently exchanges data with the remotely-powered network devices through the same network cables. Accordingly, the users of the remotely-powered network devices are not burdened with having to separately connect their devices to power sources (e.g., wall outlets). For example, the IEEE 802.3af standard, or the newer IEEE 802.3-2005 standard, which is also called the “Power over Ethernet” (PoE) standard, defines ways to build Ethernet power-sourcing equipment (PSE) and powered devices (PDs). In particular, the IEEE 802.3-2005 standard identifies ways to deliver 48 volts of Direct Current (DC) power (at up to 15.4 Watts) over unshielded twisted-pair wiring to a variety of Ethernet PDs, such as IP phones, wireless LAN access points, laptop computers and Web cameras. In accordance with the PoE standard, a PSE carries out an inline power detection process, and, if successful, an optional inline power classification process. The detection process attempts to identify a PoE-compatible PD by applying one or two DC voltages and determining if a 25K Ohm resistance is present on the line. The classification process is implemented by applying a set DC voltage and measuring the current drawn. The current drawn characterizes the PD as a member of one of a set of five PoE classes. Depending upon the class, up to a certain amount of inline power is allocated to that PD.
A new proposed standard, IEEE 802.3at, also referred to as PoE+, improves upon PoE by, inter alia, increasing the number of power classes. One way of performing the classification process under PoE+ to detect additional classes involves a repetitive classification technique, referred to as the ping pong technique. In this technique, a first PoE classification process is performed, followed by a second classification process. If the two classification processes yield different classes, then the PSE may determine that the PD is PoE+ compliant. Additional classes may be utilized by combining the results of the two classification processes and possibly further classification processes. A similar technique is described in U.S. Patent Application Publication No. 2006/0092000 (Karam, et al.), filed on Nov. 3, 2004, entitled, “POWERED DEVICE CLASSIFICATION IN A WIRED DATA TELECOMMUNICATIONS NETWORK.”